1. Field of the Invention
The present invention relates to a manufacturing method of a bossed disc-like member having a boss portion formed on one surface of the disc-like member in such a way as to project upright in the thickness direction, and to a manufacturing apparatus of the bossed disc-like member.
2. Description of the Related Art
When manufacturing a kind of disc-like member 62, in a central portion of which a boss portion 60 is formed, shown in FIG. 13, in order to form the boss portion 60 with a desired height H, it is necessary to secure capacity in the central portion of the disc-like member 62. Herein, the boss portion 60 is a portion projecting upright from a surface of the disc-like member 62 in the thickness direction of the disc-like member 62. Therefore, in order to secure the capacity in the central portion of the disc-like member 62, in a heretofore known technology, while a plurality of drawing steps are carried out, a punching step and a burring step are each carried out. However, as the plurality of drawing steps are carried out, the number of steps increases, and manufacturing cost increases. Also, as the plurality of drawing steps are carried out, a large number of drawing scores occur in the disc-like member 62, and the flatness of the disc-like member 62 decreases. Herein, the drawing scores are scores made by dies used in the drawing steps making contact.
Herein, JP-B-3-53049 discloses a technology of forming a boss portion by carrying out the drawing step and the burring step while gathering a material configuring a blank by forcibly pressing an outer periphery of the blank.